Noisy Stomp Box

[Douglas Bryant]

I use a small stomp box for adding reverb. It sounds pretty good when activated, however, if the switch is toggled to shut the reverb off, the amplified sound has a terrible hum.

Is this just the way it is with these boxes, or should the unit pass the signal thru cleanly?

Is there a way to filter out the hum?

[Brooks Montgomery]

Maybe this: Check to make sure the nuts on input and outputs are threaded tight. I had a pedal where the output unthreaded slightly and did the same thing. Tightened it up, and it went away.

[John Gould]

Much of the time it's the power supply for the pedal isn't filtered well. Causes noise and hum

[Donny Hinson]

Yup! Use batteries...or a better power supply.

[Ian Rae]

But if that's the problem surely it would hum all the time.

Like Georg says, more info please.

[Douglas Bryant]

The setup is rather simple: guitar out to reverb box in.
Out of reverb box directly to amp.

I have tried powering the unit with a battery and have used a couple of different amps --- no change (sound is good when reverb box is switched on, bad hum when box is toggled off).

Interestingly, I can greatly reduce the hum by moving the box away from other electronic devices.

My hunch is that unit does not properly shield the signal when toggled off. Oddly though is how clean it sounds when turned on.

Thank you all for your thoughts!

[Jon Light]

What's the name of the unit?

[Douglas Bryant]

Electro-Harmonix Holy Grail Neo

[Jon Light]

I currently have a Grail Nano on my board and there are no issues. But funny thing is that years ago I had an original Holy Grail -- the first model -- and it occasionally did have whine/hum issues. I recall it being a come & go problem on different pedalboards, in different pedal combinations.
Have you tried messing with the stomp switch, jiggling, pushing hard, pushing light -- seeing if the problem might be as faulty switch?

[Donny Hinson]

But if that's the problem surely it would hum all the time.

Like Georg says, more info please.

Not necessarily. Both the input and output impedances will change when the unit is switched (if the unit is a "true bypass" circuit). That change in loading could affect certain frequencies, which might make hum more/less noticeable.

But to find out if it is just a shielding problem (some stomps have plastic cases), you can wrap the unit in foil and see if that helps the problem.

Also...have you tried different cables with the unit?